JP2013053985A - Force sensor, force detection device, robot hand, and robot - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a force sensor in which a piezoelectric element is easily formed from a wafer without any waste, and its sensitivity values in an x-direction and y-direction are not different.SOLUTION: An outer peripheral shape of the piezoelectric element has at least four sides. A first side and a second side among the four sides are parallel to each other, and the remaining third side and fourth side are also parallel to each other. The distance between the first side and the second side and the distance between the third side and the fourth side are the same. An extension line of the first side and an extension line of the third line are orthogonal. Thus, pieces cut out from the same wafer can be commonly used as both of piezoelectric elements for x-direction and piezoelectric elements for y-direction. Consequently sensitivity values in the x-direction and y-direction are matched.

Description

  The present invention relates to a force sensor that detects force using a piezoelectric element made of a piezoelectric material such as quartz.

  In a force sensor using the piezoelectric effect of a single crystal such as quartz, the applied force component is decomposed and detected by the anisotropy of the piezoelectric effect depending on the crystal orientation. A crystal piezoelectric force sensor using such a crystal piezoelectric element has a structure in which a plurality of crystal piezoelectric elements are overlapped between two plates, and the force is received by two plates and transmitted to the crystal piezoelectric element. The force component applied to the crystal piezoelectric element is detected. Specifically, the plurality of crystal piezoelectric elements are classified into three types, and crystal piezoelectric elements (z-direction crystal piezoelectric elements) having sensitivity to a force in the vertical direction (z direction) and horizontal directions (x Crystal piezoelectric element (x-direction crystal piezoelectric element) sensitive to the force in the direction), and crystal piezoelectric element (y-direction crystal piezoelectric element) sensitive to the force in the horizontal direction (y direction) orthogonal to the x direction. The applied force is decomposed into force components in the xyz direction and detected.

  The quartz crystal piezoelectric element in the conventional quartz piezoelectric force sensor has been formed in a disk shape (see Patent Document 1) or a washer shape. In addition, as a quartz crystal piezoelectric element used as a piezoelectric vibration element instead of a force sensor, there is a rectangular piezoelectric element (see Patent Document 2).

Japanese Unexamined Patent Publication No. Hei 4-231827 JP 2009-135830 A

  However, in the case of a disk shape or a washer shape, when the crystal piezoelectric element is cut out from the wafer and formed, there is a problem that it cannot be formed without waste because the outer peripheral shape is circular. Also, when assembling a force sensor by superimposing crystal piezoelectric elements, especially for horizontal crystal piezoelectric elements (x-direction crystal piezoelectric elements, y-direction crystal piezoelectric elements), the crystal orientation of the crystal piezoelectric element is It has been very difficult to assemble accurately according to the direction of the force component to be detected (that is, the x direction and y direction).

  On the other hand, in the case of a rectangular shape, when the crystal piezoelectric element is formed from a wafer, it can be easily formed without waste simply by cutting the wafer in a straight line. However, when such rectangular crystal piezoelectric elements are superposed to form a force sensor, the crystal orientation of the horizontal crystal piezoelectric elements (the crystal piezoelectric element for x direction and the crystal piezoelectric element for y direction) needs to be different. For this reason, it is necessary to cut out the x-direction crystal piezoelectric element and the y-direction crystal piezoelectric element from separate wafers. As a result, there is a problem that the sensitivity of the force sensor differs between the x direction and the y direction.

  The present invention has been made in order to solve at least a part of the above-described problems of the prior art. The piezoelectric element can be easily formed from a wafer, and the sensitivity in the x direction and the y direction is improved. It is an object to provide a force sensor that does not cause a difference.

In order to solve at least a part of the problems described above, the force sensor of the present invention employs the following configuration. That is,
A force sensor formed by laminating a plurality of piezoelectric elements made of piezoelectric material and a plurality of electrode plates,
The outer peripheral shape of the piezoelectric element is
Has at least four sides,
The first side and the second side of the four sides are parallel to each other, and the third side and the fourth side of the four sides are parallel to each other,
The distance between the first side and the second side is equal to the distance between the third side and the fourth side,
The extension line of the first side and the extension line of the third side are orthogonal to each other.

  A piezoelectric element having such an outer peripheral shape can be easily formed by simply cutting the wafer in a straight line when forming the piezoelectric element from the wafer. Further, when the direction perpendicular to the stacking direction in which the piezoelectric element and the electrode plate are stacked is the x direction and the y direction (where the y direction is a direction perpendicular to the x direction), 90 cut from the same wafer is used. It can be used in common as an x-direction piezoelectric element having sensitivity to an x-direction force and a y-direction piezoelectric element having sensitivity to a y-direction force. Therefore, the sensitivity in the x direction and the y direction can be made uniform.

  Further, in the above-described force sensor of the present invention, the outer peripheral shape of the piezoelectric element can be a shape obtained by cutting a corner from a square, but is preferably a square.

  If the outer peripheral shape of the piezoelectric element is square, it can be easily cut out from the wafer. In addition, if it is a square, it will be exactly the same shape when rotated 90 degrees, so it is easy to stack while aligning the x-direction piezoelectric element and the y-direction piezoelectric element by rotating 90 degrees. It becomes possible to do.

  In the force sensor of the present invention described above, the piezoelectric elements and the electrode plates are alternately stacked, and the piezoelectric elements are in contact with the adjacent electrode plates at the central portion of the outer peripheral shape of the piezoelectric elements, and the contact surface is circular or washer. You may make it form. For example, the central portion of the piezoelectric element may be projected in a circular shape or a washer shape, and may be in contact with the electrode plate at the top surface of the projected portion. Or conversely, the central portion of the electrode plate may be projected in a circular or washer shape. Furthermore, a circular or washer-shaped electrode plate may be sandwiched between the piezoelectric elements.

  In this way, when a force is applied to the force sensor, the piezoelectric element receives a force on the circular or washer-shaped contact surface, so that no stress concentration occurs. As a result, it is possible to improve the resistance against the destruction of the piezoelectric element.

In the force sensor of the present invention described above, the piezoelectric element is a specific piezoelectric element having sensitivity to a force in a direction perpendicular to the stacking direction in which the piezoelectric element and the electrode plate are stacked (for example, for the x direction described above). A mark indicating the direction of sensitivity may be formed on the specific piezoelectric element.
In this way, it is possible to easily stack and arrange each piezoelectric element with the crystal orientation necessary for force detection.

In the force sensor of the present invention described above, the direction in which the specific piezoelectric element has sensitivity may be a direction parallel to the first side or the third side.
If it does in this way, it will become possible to laminate | stack each piezoelectric element easily, aligning the direction which has a sensitivity.

Further, in the above-described force sensor of the present invention, the piezoelectric element is sensitive to the force in the x direction with respect to the three axes in the x, y, and z directions orthogonal to each other, and the y direction piezoelectric element. It may include a y-direction piezoelectric element that is sensitive to force and a z-direction piezoelectric element that is sensitive to z-direction force, and may be able to detect a triaxial force.
If it does in this way, it will become possible to detect the force of a triaxial direction with one force sensor.

The force detection device of the present invention may include two or more force sensors as described above, and may detect a moment around a desired axis.
In this way, not only the axial force component but also the moment around the axis can be easily detected.

  Further, in the above-described force detection device, three or more force sensors are provided so as not to be arranged on the same straight line so that the force in the three axis directions and the moment around the three axes can be detected. Also good.

  In this way, the force in the triaxial direction and the moment about the triaxial direction can be detected, so that it can be suitably used as a sensor mounted on, for example, a robot or various machines.

Moreover, it is good also as operating a robot hand or a robot using the force detection apparatus comprised including two or more force sensors of this invention.
As described above, the force detection device including two or more force sensors of the present invention can easily detect not only the axial force component but also the moment around the axis. For this reason, if the robot hand or robot is operated by mounting the force detection device of the present invention, a small and high performance robot hand or robot can be realized.

It is the disassembled perspective view which showed the structure of the force sensor of a present Example. It is explanatory drawing which showed typically the cross section of the force sensor shown in FIG. It is explanatory drawing which shows the shape of the crystal piezoelectric element in FIG. It is a perspective view which shows the external appearance of the force detection apparatus provided with four force sensors. It is explanatory drawing which shows the robot hand and robot which mount the force detection apparatus of a present Example.

Hereinafter, in order to clarify the contents of the present invention described above, examples will be described in the following order.
A. Force sensor configuration:
B. Force sensor operation:
C. Configuration and operation of force detector:
D. Variations:

A. Force sensor configuration:
FIG. 1 is an exploded perspective view showing the structure of the force sensor 100 of the present embodiment. As shown in FIG. 1, the force sensor 100 includes a plurality of alternately laminated electrode plates 106 and crystal piezoelectric elements 108 formed of a crystal plate having a square outer periphery between an upper plate 102 and a lower plate 104. Configured. For the electrode plate 106, a metal having conductivity, for example, a simple substance or an alloy such as titanium, aluminum, copper, or iron can be used. For example, stainless steel can be used as the iron alloy, and it is preferably used because of its excellent durability and corrosion resistance. In addition to one crystal piezoelectric element 108, one fluororesin spacer 110 is sandwiched between two adjacent electrode plates 106. A square through hole is opened at the center of the fluororesin spacer 110, and the crystal piezoelectric element 108 is positioned in the through hole, whereby the crystal piezoelectric element 108 is positioned in the xy plane.

  Two through holes 116 are opened in the upper plate 102. Each electrode plate 106 and each fluororesin spacer 110 each have two circular through holes. On the other hand, two fluororesin sleeves 112 having a cylindrical pipe shape are disposed between the upper plate 102 and the lower plate 104. When laminating each electrode plate 106 and each fluororesin spacer 110 between the upper plate 102 and the lower plate 104, two circular through holes respectively provided in the electrode plate 106 and the fluororesin spacer 110 are provided with 2 The two fluororesin sleeves 112 are laminated so as to penetrate each other. Then, two pressurizing bolts 114 are inserted into the through-hole 116 from above the upper plate 102, inserted into the fluororesin sleeve 112, and screwed into the lower plate 104. Thereby, each electrode plate 106 and each fluororesin spacer 110 are positioned in the xy plane, and a constant pressure is applied to each electrode plate 106 and each crystal piezoelectric element 108 in the z direction.

  FIG. 2 is an explanatory view schematically showing a cross section of the force sensor 100 shown in FIG. As shown in FIG. 2, between the upper plate 102 and the lower plate 104, precisely, seven electrode plates 106a to 106g and six crystal piezoelectric elements 108a to 108f are laminated.

  Of the seven electrode plates 106a to 106g, the electrode plates 106b, 106d, and 106f are each connected to an output signal line. The electrode plates 106a, 106c, 106e, and 106g are grounded.

  On the other hand, among the six crystal piezoelectric elements 108a to 108f, the two middle crystal piezoelectric elements 108c and 108d are crystal piezoelectric elements (z-direction crystal piezoelectric elements) that are sensitive to the force in the compression direction, that is, the z direction. Yes, it consists of a so-called X-plate crystal plate. The X direction of the crystal is along the z direction as indicated by the arrow, and the quartz crystal element 108c located above and the quartz crystal element 108d located below are opposite to each other. The lower two crystal piezoelectric elements 108e and 108f are crystal piezoelectric elements (x-direction crystal piezoelectric elements) having sensitivity to the force in the x direction in the horizontal direction. The X direction of the crystal is along the x direction as shown by the arrow, and the upper quartz piezoelectric element 108e and the lower quartz piezoelectric element 108f are opposite to each other. The upper two crystal piezoelectric elements 108a and 108b are crystal piezoelectric elements (a crystal piezoelectric element for y direction) having sensitivity to a force in the y direction in the horizontal direction. The X direction of the quartz crystal is along the y direction as indicated by a symbol, and the quartz crystal element 108a located above and the quartz crystal element 108b located below are opposite to each other.

  FIG. 3 is an explanatory view showing the shape of the quartz crystal piezoelectric element 108 in FIG. FIG. 3A is a plan view showing the crystal piezoelectric element 108 from above, and FIG. 3B is a side view showing the side surface of the crystal piezoelectric element 108. As shown in FIG. 3, in this embodiment, each of the quartz crystal piezoelectric elements 108 (that is, 108a to 108f) is composed of a quartz plate having a square outer periphery as described above (see FIG. )). Further, a pressure receiving portion 132 having a circular pressure receiving surface 134 on the top surface is formed at the center of the quartz crystal piezoelectric element 108, and is formed in a mesa shape as a whole. Therefore, when the quartz crystal piezoelectric element 108 is disposed between the two electrode plates 106, the one electrode plate 106 comes into contact with the circular pressure receiving surface 134. A mark 136 indicating the crystal orientation of the crystal (in this case, the X direction of the crystal) is marked on the corner surface of the crystal piezoelectric element 108. The mark 136 is formed at the same time when the pressure receiving portion 132 is formed on the quartz crystal piezoelectric element 108.

B. Force sensor operation:
When a force is applied to the force sensor 100, the upper plate 102 and the lower plate 104 receive the force and transmit the force to the crystal piezoelectric elements 108a to 108f. Each of the quartz crystal piezoelectric elements 108a to 108f detects a force component corresponding to the crystal orientation of the quartz crystal by the piezoelectric effect. That is, as shown in FIG. 2, in the y-direction crystal piezoelectric elements 108a and 108b, as described above, since the X direction of the crystal is along the y direction, the force component in the y direction is detected, and the detected value is The electric signal based on this is output as an Fy signal from the electrode plate 106b to the output signal line. Similarly, in the crystal piezoelectric elements 108c and 108d for z direction, since the X direction of the crystal is along the z direction, a force component in the z direction is detected, and an electric signal based on the detected value is used as an Fz signal. Output to the output signal line from 106d. In the x direction crystal piezoelectric elements 108e and 108f, since the X direction of the crystal is along the x direction, a force component in the x direction is detected, and an electric signal based on the detected value is output as an Fx signal from the electrode plate 106f. Output to the signal line.

  In the force sensor 100 in this embodiment, since the outer peripheral shape of the crystal piezoelectric element 108 is square, when the crystal piezoelectric element 108 is formed from a wafer, it can be easily formed without waste simply by cutting the wafer in a straight line. it can. In addition, since the outer peripheral shape is a square, the same wafer cut into a square can be rotated by 90 degrees and used as the x-direction crystal piezoelectric elements 108e and 108f and the y-direction crystal piezoelectric elements 108a and 108b. Can be used. Therefore, in the force sensor 100, the sensitivity in the x direction and the y direction can be made uniform. Further, since the outer peripheral shape of the quartz crystal piezoelectric element 108 is square and the mark 136 indicating the crystal orientation of the quartz crystal is marked on the surface of the quartz crystal piezoelectric element 108, each crystal piezoelectric element 108 has a crystal orientation necessary for force detection. And can be easily stacked and arranged. In addition, a pressure receiving portion 132 having a circular pressure receiving surface 134 is formed at the center of the quartz piezoelectric element 108, and when a force is applied to the force sensor 100, the quartz piezoelectric element 108 is forced by the circular pressure receiving surface 134. Therefore, stress concentration does not occur and resistance to breakage can be improved.

  Note that the force sensor 100 has an operation principle of detecting an electric charge generated in the quartz plate by receiving an external force with an electrode. From the viewpoint of efficiently detecting the charge generated in the quartz plate, the structure in contact with the electrode by the circular pressure receiving surface 134 provided at the center of the quartz piezoelectric element 108 as in this embodiment is the same as the quartz plate. Since the contact area with an electrode plate will become narrow, it is not necessarily preferable. However, the force sensor 100 is subjected to a large load, and it is important to improve the resistance against the destruction of the quartz crystal piezoelectric element 108. In view of this, in this embodiment, from the viewpoint of improving the resistance to breakage, a structure is adopted in which the crystal plate and the electrode plate are brought into contact with each other through a circular contact surface (that is, the pressure receiving surface 134) at the center portion.

C. Configuration and operation of force detector:
FIG. 4 is a perspective view showing an appearance of a force detection device 200 including four force sensors 100 shown in FIG. As shown in FIG. 4, in the force detection device 200, the upper plate 102 and the lower plate 104 each have a disk shape, and are shared by the force sensors 100 a to 100 d. The force sensors 100a to 100d are arranged 90 degrees apart from each other along the circumference, and the three or more force sensors 100 are arranged so as not to line up on the same straight line.

  As described above, the force sensor 100 can detect a force applied to the force sensor 100 in a state where the force sensor 100 is decomposed into force components in the xyz direction. Therefore, the force detection device 200 can detect a moment in one direction by combining any two force sensors 100. Moreover, since the force detection device 200 uses three or more force sensors 100 and is arranged so that the force sensors 100 do not line up on the same straight line, the force in the triaxial direction and the moment about the triaxial direction Can be detected simultaneously.

D. Variations:
The force sensor 100 and the force detection device 200 according to the present embodiment have been described above. However, the present invention is not limited to all the embodiments described above, and can be implemented in various modes without departing from the scope of the present invention. It is.

  For example, in the embodiment described above, the outer peripheral shape of the quartz crystal piezoelectric element 108 is a square, but may be a shape in which square corners are notched, for example, a hexagon or an octagon. Any shape may be used as long as at least a part of each of the four sides of the square remains.

  In the embodiment described above, the pressure receiving portion 132 formed at the center of the quartz crystal piezoelectric element 108 has a circular pressure receiving surface 134, but may be a washer shape instead of a circular shape. As described above, even when the force is received by the washer-shaped pressure receiving surface 134, the stress concentration is small, and the resistance to breakage is improved.

  In the above-described embodiment or modification, in order to improve the resistance against the destruction of the quartz piezoelectric element 108, the pressure receiving portion 132 in which the pressure receiving surface 134 is circular or washer-shaped is formed at the center of the quartz piezoelectric element 108. However, a convex portion in which the contact surface with the crystal piezoelectric element 108 forms a circular shape or a washer shape may be formed in the center of the electrode plate 106 adjacent to the crystal piezoelectric element 108. This configuration also reduces stress concentration on the quartz crystal piezoelectric element 108 and improves resistance to breakage.

In the embodiment described above, quartz is used as the piezoelectric material constituting the piezoelectric element, but the present invention is not limited to this. As the piezoelectric material, in addition to quartz, titanate ceramics such as lead zirconate titanate (PZT) and barium titanate (BaTiO ₃ ), lithium niobate (LiNbO ₃ ), and zinc oxide (ZnO) are preferable. Used for.

  Further, as illustrated in FIG. 5, the robot hand 300 or the robot 400 may be configured using the force detection device 200 of the present embodiment. Since the force detection device 200 of the present embodiment can measure not only the axial force but also the moment about the axis, it is possible to realize a small and high-performance robot hand or robot.

100 ... Force sensor, 102 ... Upper plate, 104 ... Lower plate,
106 ... Electrode plate, 108 ... Quartz piezoelectric element, 110 ... Fluorine resin spacer,
112 ... Fluororesin sleeve, 114 ... Pressurizing bolt, 116 ... Through hole,
132 ... pressure receiving part, 134 ... pressure receiving surface, 136 ... mark,
200 ... Force detection device

Claims (10)

A force sensor formed by laminating a plurality of piezoelectric elements made of piezoelectric material and a plurality of electrode plates,
The outer peripheral shape of the piezoelectric element is
Has at least four sides,
The first side and the second side of the four sides are parallel to each other, and the third side and the fourth side of the four sides are parallel to each other,
The distance between the first side and the second side is equal to the distance between the third side and the fourth side,
The force sensor, wherein the extension line of the first side and the extension line of the third side are orthogonal to each other.   The force sensor according to claim 1, wherein an outer peripheral shape of the piezoelectric element is a square. The force sensor according to claim 1 or 2,
The piezoelectric elements and the electrode plates are alternately stacked,
The piezoelectric element is in contact with the adjacent electrode plate at a circular or washer-shaped contact surface in a central portion of the outer peripheral shape of the piezoelectric element. A force sensor according to any one of claims 1 to 3,
The piezoelectric element includes a specific piezoelectric element having sensitivity to a force in a direction perpendicular to a stacking direction in which the piezoelectric element and the electrode plate are stacked, and the specific piezoelectric element indicates the direction of the sensitivity. A force sensor characterized in that a mark is formed. A force sensor according to any one of claims 1 to 4,
The piezoelectric element includes a specific piezoelectric element having sensitivity to a force in a direction perpendicular to a stacking direction in which the piezoelectric element and the electrode plate are stacked, and the direction of sensitivity of the specific piezoelectric element is the first direction. A force sensor characterized by being in a direction parallel to the side or the third side. A force sensor according to any one of claims 1 to 5,
For the three axes in the x, y, and z directions orthogonal to each other, the piezoelectric element includes an x direction piezoelectric element that is sensitive to x direction force and a y direction piezoelectric element that is sensitive to y direction force. And a z-direction piezoelectric element having sensitivity to the z-direction force, and detecting the triaxial force. A force detection device for detecting an applied force,
A force detection device comprising two or more force sensors according to claim 6 and detecting a moment about a desired axis. The force detection device according to claim 7,
Three or more force sensors are arranged so as not to line up on the same straight line, and the force in the three-axis direction and the moment about the three axes are detected.   A robot hand that operates using the force detection device according to claim 7.   A robot that operates using the force detection device according to claim 7.

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